Excel Sharepoint Data Refresh - Can't refresh your data

[cmncp]

I have an excel file in Sharepoint Online, which has a simple table of data.  Using Power BI Desktop, I can connect to it and create a report.  After I publish the report to Power BI Service, I can see the report, and it all looks good.  However, as soon as I try to refresh the Dataset, I get the following error:

Can't refresh your data

The credentials you provided for the data source are invalid. Please check the credentials for all the data sources.
Please try again later or contact support. If you contact support, please provide these details.

When I close the message, it takes me to the Settings page for the dataset and the Data source credentials section.  It says:

Your data source can't be refreshed because the credentials are invalid. Please update your credentials and try again.

When I click on Edit Credentials, the only Authentication method available is "WindowsWithoutImpersonation".  When I click Sign In, it just sits there spinning and never comes back.

Any ideas what I am doing wrong?